In the ASOTRACE log and in the AP Msg window these messages are displayed:
10:50:17 AXC0301E Input: MSGID(IEE772)
10:50:17 AXC0316W Invalid Session name Session1
10:50:17 AXC0316W Invalid Session name Session2
The messages mean that sessions Session1 and Session2 are not defined or enabled in the active session definition set. If an AP rule contains multiple SESSION keyword definitions, AP requires that all sessions defined by the SESSION keyword for the rule be defined and enabled otherwise it ignores the rule.
When a session is removed, or disabled, you also need to check if there are rules defined against them, or else they will fail.
Not only for the specific session, but also for the other sessions defined at that specific rule.